1. Field of the Invention
This invention relates to an electric power steering device for motor vehicles.
2. Prior Art
The electric power steering device for motor vehicles is equipped with a mechanism which transmits the rotation of a steering shaft rotated by the operation of a steering wheel, to a rack shaft through a pinion, thereby steering vehicle driving wheels through a tie rod connected to either end of the rack shaft. Furthermore an auxiliary motor for steering device is equipped. With the detection of a steering torque produced at the steering shaft, the motor is excited in accordance with a signal of the detection. The driving torque of the motor is transmitted to a steering rack shaft, to thereby assist the steering force of the steering wheel.
For the electric power steering device of the above constitution, there have been proposed various kinds of configurations as seen in Japanese Laid Open Patent Publication No. H7-165089, Japanese Laid Open Patent Publication No. H8-301130, Japanese Laid Open Patent Publication No. H10-95354, and Japanese Laid Open Patent Publication No. 2000-168581. One example of configurations of such prior art electric power steering devices will be explained by referring to FIG. 3.
FIG. 3 is a sectional view that shows a major portion of the configuration of the steering rack shaft and motor section of the electric power steering device. In FIG. 3, numeral 101 denotes a steering rack shaft; and 102 represents a steering shaft. The steering shaft 102 is fitted with an unillustrated pinion, which meshes with the teeth of the rack on the rack shaft 101.
In FIG. 3, a screw 107b of a later-described ball nut mechanism is formed on the left side of the rack shaft 101. Further the left end of the rack shaft 101 is connected with a tie rod not shown.
Numerals 103 and 104 denote housings. A first housing 103 and a second housing 104 are so constituted as to be separably connected at the part A. In the first housing 103 is mounted a later-described motor for assisting the steering force. In the second housing 104 a later-described ball nut mechanism 107 is arranged. The rack shaft 101 is penetrated through the inside of the first housing 103 and the second housing 104, and axially slidably supported.
Numeral 105 represents a motor mounted coaxially with the rack shaft 101 to assist the steering force. A stator 105a is fixedly mounted in the first housing 103, while a rotor 105b is coaxially mounted outside of the rack shaft 101 and is rotatably supported by bearings 106a and 106b inside of the first housing 103.
Numeral 107 denotes a ball nut mechanism, which includes a hollow cylindrical nut 107a provided with an internal groove of an approximately semicircular form in cross section on the inner surface, a screw 107b with an external groove of an approximately semicircular form in cross section on the outer surface of the rack shaft 101, and a number of balls 107c recirculating, while rolling, in the spiral groove formed by the inner and external grooves.
The nut 107a of the ball nut mechanism 107 is rotatably supported by on a bearing 108 mounted inside of the second housing 104.
In FIG. 3, inside the right end portion of the nut 107a are formed internal spline grooves 107s, which mesh with spline teeth 105s formed on the left end portion of the rotor 105b of the motor 105 as shown in FIG. 3. The nut 107a and the rotor 105b are connected as one body in the direction of rotation and slidably splined in the axial direction.
The rack shaft 101 is axially slidably supported at only two positions: at an unillustrated guide which is located in a section where a pinion provided on a steering shaft 102 meshes with the rack teeth formed on the rack shaft 101, and at the ball nut mechanism 107.
When, in the above-described constitution, the electric current determined in accordance with the steering torque is supplied to the motor 105, the rotor 105b turns to thereby turn the nut 107a of the ball nut mechanism 107 which is splined with the rotor 105b. The rotation of the nut 107a axially moves the rack shaft 101, thus operates the steering mechanism through the tie rod.
The above-described prior-art electric power steering device is assembled by the following procedure. That is, first the stator 105a of the motor 105 is secured in the first housing 103, and then the bearings 106a and 106b are set in the first housing 103, to thereby rotatably support the rotor 105b of the motor 105.
Furthermore, the bearing 108 is set in the second housing 104, to thereby rotatably support the nut 107a of the ball nut mechanism 107.
Next, the first housing 103 and the second housing 104 are jointed at the portion A. At this time, the nut 107a and the rotor 105b are adjusted in position so as to be in the same phase in the direction of rotation so that the inner spline grooves 107s formed in the right end portion of the nut 107a shown in FIG. 3 and the spline teeth 105s formed on the left end portion of the rotor 105b shown in FIG. 3 will mutually mesh, and that the nut 107a and the rotor 105b will be splined simultaneously with the connection of the housing section.
According to the prior-art constitution, the two component members, that is, the outer housing section and the members arranged in the housing, are simultaneously connected. Besides, at the time of this connection, these two members arranged in the housing need phase adjustment in the direction of rotation and then are connected. This procedure is complicated and hard to perform, and therefore will be of low working efficiency. This invention, therefore, is intended to cope with the above-described disadvantage.
1. A primary object of this invention is to provide a new electric power steering device capable of easily mounting and assembling, a power transmission device including a plurality of members which transmit the rotation of the motor for assisting the steering force, to the steering shaft through a ball nut mechanism.
2. Another object of this invention is to provide a new and easy-to-assemble electric power steering device of the following construction. The housing is separated into a first chamber and a second chamber. In the first chamber, the motor for assisting the steering force is inserted from one end of the housing. In the second chamber, a rack shaft assembly including a rack shaft to be connected to the steering shaft and a ball screw mechanism is inserted from the other end of the housing. The rotor of the motor for assisting the steering force and the rack shaft are connected through the ball screw mechanism so that the rack shaft will pass through the first and second chambers.
3. Further another object of this invention will be clearer from the detailed description of the preferred embodiments with reference to the accompanying drawings.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.